Photonic devices and microphotonics provide exciting potential for furthering the advancement of technology historically served by microelectronics. Photonic devices may be used as frequency selection filters to enable large volumes of data to travel along optical fibers and to be routed to their final destinations. As light traveling in a fiber is incident upon a frequency selection photonic crystal, the light at the desired wavelength travels through the photonic crystal and is routed to its destination, while the light at all other frequencies is reflected. Currently, photonic crystals are commonly manufactured with layered GaAs and AlGaAs or layered Si and SiO2. Microphotonic devices are expected to replace microelectronic devices once cost-effective methods of manufacturing photonic devices are developed. One reason that optical circuits have not been widely implemented is that there are manufacturing problems related to making photonic devices meet index of refraction specifications.
Lasers may be used to drill holes in or otherwise machine a work piece, including, glass or silicon or other dielectric materials to form waveguides or microoptical structures in the materials. The behavior of light in a photonic crystal may be better understood by analogy to the behavior of electricity in a conventional crystal. Crystals are characterized by a periodic arrangement of atoms or molecules. The lattice of atoms or molecules may introduce gaps in the energy band structure of the crystal through which electrons cannot propagate. A photonic crystal is a lattice of discontinuities in the refractive index of a material. One example is a lattice of holes in a waveguide. If the dielectric constants of the waveguide material and the material in the holes is sufficiently different, light is substantially confined by the interfaces. Scattering of the light at the interfaces can produce many of the same effects for photons as are produced for electrons by the lattice of atoms or molecules.
Photonic crystal fabrication precisely aligns the holes that constitute the photonic crystal in the described lattice structure. Current laser micromachining methods, such as direct writing, do not provide a way to drill features with the sub-micron accuracy and precision needed for photonic crystals. This is because it is difficult to accurately align the laser beam or to produce multiple holes positioned in the desired lattice arrangement with an accuracy that is desirable to produce an effective photonic structure. The current method of producing holes (single and multiple holes) uses a moveable work piece holder on which a photonic crystal is mounted. The laser beam is aligned at the desired location(s) on the crystal by maintaining the laser beam in a single location and moving the work piece holder with the work piece mounted onto it. The problem is that the holder cannot be moved with a level of accuracy suitable for manufacturing photonic crystals. In addition to the spatial positioning errors, photonic structures may also suffer from blurring of the image of the laser beam as the feature sizes decrease to less than or equal to the size of the wavelength of the beam. What is needed is a way to mass manufacture a photonic crystal within specifications, including a way to align the beam and work piece in a laser drilling system for drilling holes in a photonic crystal where the feature size is less than or equal to the wavelength of the drilling laser beam.